Archived posting to the Leica Users Group, 2003/11/03
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Clive Moss <chmphoto@sbcglobal.net> said: > [...] switch it to Greyscale using Image>Mode [....] What I do not > understand is if I am losing information. To be pedantic for a moment: information has been lost because it is no longer possible to convert the grayscale image back to color. Of course, this is obvious. And, equally obvious is that, if you convert the image to grayscale using any formula you choose, once you "bake out" the data as 8-bit per pixel samples, you are in the same situation. The only difference is that the grayscale pixels will have different values from one conversion formula to the next. There are many color->grayscale conversion formulas available. No one is the "best" for all situations. The 601 and 709 specifications are designed for television broadcast, so that the Y channel holds a grayscale signal that is compromised by two (similar) goals: to provide a pleasant image for viewers on monochrome televisions; and to provide a good luminance signal, that is overlayed by the color components, for color viewers. The Photoshop Image->Mode conversion may be based on one of these television formulas, and similarly for in-camera mode conversion. As such, it is probably wise to avoid using this conversion, since better options, which give more control to you, are available. (Not to mention that the TV formulas probably don't match the spectral mix that panchromatic film (coupled with color filters) has. That's the main reason Image->Mode conversions don't look like b&w film shots.) The best thing is to make a "Channel Mixer" layer on top of your color image, in Photoshop. It not only affords you the ability to pick exactly the mix of RGB that you want, but you can return to tweak the mix whenever you want. You should save this as your "work" file. With some experimentation, you can probably derive the exact color mixer settings to mimic tri-x and a tiffen yellow filter, or whatever you prefer. However, when you finally decide to "flatten" the image into a final grayscale for printing, you are throwing away information your original color shot contains. But, you have more control over how the data is converted. Mike - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html